Don't use that calculator.
It will give you very misleading results because it doesn't consider the rising difficulty.
If you use that calculator, you will have to calculate two times. One with current difficultly and the another with increased difficulty(+10%)
[1]. My personal favourite is
http://vnbitcoin.org/bitcoincalculator.php.
[1] +10% difficulty isn't accurate but we can get an approximate result.
P.S. I found another with better results,
https://bitcoinwisdom.com/bitcoin/difficulty.
-MZ